1. Field of the Invention
The present invention relates to a cooling fan assembly for an electronic apparatus and, more particularly, to such a cooling fan assembly with low-noise characteristics.
2. Description of Related Art
It is well known that electronic elements such as semiconductors used in electronic apparatuses have been developed greatly. As the development of semiconductor devices increasingly progresses, the working performance and the computation speed are greatly enhanced. However, volumes of such semiconductor-based devices, such as central processing units (CPUs) or other electronic devices in, e.g., computer systems, also tend to become smaller and smaller. Due to the accelerated data processing speed, the accompanying working temperature may become significantly high. Such a high temperature is liable to degrade computation efficiency and even damage the electronic apparatuses, if allowed to go unchecked. In order to effectively lower the high working temperature, heat-dissipating devices (e.g., heat sinks and/or cooling fans) are generally required for CPUs and other electronic devices.
FIG. 5 (Prior Art) represents a conventional cooling fan assembly 4 for dissipating heat from an electronic apparatus (not shown). The cooling fan assembly 4 includes a casing 40 and a fan 42 accommodated therein. The casing 40 includes a volute tongue 400, an air inlet 402, a volute chamber 404, and an air outlet 406. The fan 42 is a centrifugal fan and includes a wheel 420 and a plurality of wheel blades 422 secured with the wheel 420.
The wheel blades 422 are driven by the wheel 420 and rotate counter clockwise. Airflow enters the cooling fan assembly 4 through the air inlet 402 and airflow is blown out by the wheel blades 422, through the air outlet 406. The airflow pressure is increased because the airflow impacts the volute tongue 400. The airflow blows along with the volute chamber 404 so that kinetic energy of the airflow converts to pressure energy and makes static pressure of the airflow great enough to surmount the air resistance outside the casing 40. Hereafter, most of the airflow directly blows outside the casing 40 through the air outlet 406, while the rest of the airflow is pushed, by the wheel blades 422, towards the volute tongue 400. An area adjacent the volute tongue 400 becomes a high-pressure area, while the area of the air outlet 406 is a low-pressure area. Thereby, it is reasonable that the airflow blows back from the volute tongue 400 to the air outlet 406. With the help of the cooling fan assembly 4, the airflow blowing out through the air outlet 406 cools the electronic apparatus to some degree. However, the cooling airflow that blows from the cooling fan assembly 4 is somewhat insufficient because only a single fan 42 is employed. Furthermore, high-level noise occurs because the airflow fiercely impacts the volute tongue 400, which is formed by part of the casing 40, i.e. it is tangible.
In order to overcome above-mentioned disadvantages which the cooling fan assembly 4 bearing, another conventional cooling fan assembly 6, as shown in FIG. 6 (Prior Art), is presented. The cooling fan assembly 6 includes a casing 60 and two centrifugal fans 62 and 64. The casing 60 is substantially symmetrically divided into a pair of volute chambers 602a and 602b by a partition 600. The casing 60 includes a pair of air inlets 604a and 604b, a pair of air outlets 606a and 606b, and a pair of volute tongues 608a and 608b. The pair of volute chambers 602a and 602b is independent of one another. The pair of air outlets 606a and 606b is juxtaposed at a same side of the casing 60, as well as the pair of the volute tongues 608a and 608b. The pair of centrifugal fans 62 and 64, respectively, is received in the pair of volute chambers 602a and 602b and adjacent to the pair of air outlets 606a and 606b. The centrifugal fan 62 includes a wheel 620 and a plurality of wheel blades 622 secured with the wheel 620. Similarly, the centrifugal fan 64 includes a wheel 640 and a plurality of wheel blades 642 secured with the wheel 640.
The centrifugal fan 62 rotates clockwise, and, on the contrary, the centrifugal fan 64 rotates counter clockwise. Airflow enters the casing 60 through the pair of air inlets 604a and 604b and then is pushed by the fans 62 and 64. Most of the airflow directly blows outside the casing 60 through the pair of air outlets 606a and 606b, respectively, yet the rest of the air is pushed towards the volute tongues 608a and 608b by the wheel blades 622 and 642. It is reasonable that the airflow blows back from the volute tongues 608a and 608b and to the air outlets 606a and 606b, respectively, because the area adjacent the volute tongues 608a and 608b are high-pressure areas, while the areas in which the air outlets 606a and 606b are located are low-pressure areas. Volumes of the airflow blowing to dissipate the heat associated with the correlative electrical apparatus are doubled since the cooling fan assembly 6 is furnished with a pair of fans 62 and 64.
However, the cooling fan assembly 6 is actually simply scrabbled up by the two single fans 62 and 64, since the partition 600 is configured for dividing the casing 60 into two individual portions. Although the volume of the airflow blowing out is doubled, the noise is still at a high level because the airflow fiercely impacts the pair of volute tongues 608a and 608b formed by parts of the casing 60.
Accordingly, what is needed is a cooling fan assembly, which readily dissipates heat from the electronic apparatus and does so with low-noise characteristics.